命名空间： System.Collections.Generic
程序集： System（在 System.dll 中）
备注
示例
继承层次结构
程序集： System（在 System.dll 中）
备注 队列在按接收顺序存储消息方面非常有用，以便于进行顺序处理。存储在 Queue<(Of <(T>)>) 中的对象在一端插入，从另一端移除。
Queue<(Of <(T>)>) 的容量是指 Queue<(Of <(T>)>) 可以容纳的元素数。当向 Queue<(Of <(T>)>) 添加元素时，将通过重新分配内部数组，根据需要自动增大容量。可通过调用 TrimExcess 来减少容量。
Queue<(Of <(T>)>) 接受 nullNothingnullptrnull 引用（在 Visual Basic 中为 Nothing） 作为引用类型的有效值并且允许有重复的元素。
示例 下面的代码示例演示了 Queue<(Of <(T>)>) 泛型类的几个方法。此代码示例创建一个具有默认容量的字符串队列，并使用 Enqueue 方法对五个字符串进行排队。枚举队列元素，这不会更改队列的状态。使用 Dequeue 方法使第一个字符串出列。使用 Peek 方法查找队列中的下一项，然后使用 Dequeue 方法使该项出列。
使用 ToArray 方法创建一个数组并将队列元素复制到该数组，然后将该数组传递给接受 IEnumerable<(Of <(T>)>) 的 Queue<(Of <(T>)>) 构造函数以创建队列副本。将显示副本的元素。
创建一个大小是队列大小两倍的数组，并使用 CopyTo 方法从数组中间开始复制数组元素。再次使用 Queue<(Of <(T>)>) 构造函数创建第二个队列副本，此队列在开始处包含三个 null 元素。
使用 Contains 方法显示字符串“four”在第一个队列副本中，然后使用 Clear 方法清除此副本并由 Count 属性显示该队列为空。
using System;
using System.Collections.Generic;
class Example
{
public static void Main()
{
Queue<string> numbers = new Queue<string>();
numbers.Enqueue("one");
numbers.Enqueue("two");
numbers.Enqueue("three");
numbers.Enqueue("four");
numbers.Enqueue("five");
// A queue can be enumerated without disturbing its contents.
foreach( string number in numbers )
{
Console.WriteLine(number);
}
Console.WriteLine("\nDequeuing '{0}'", numbers.Dequeue());
Console.WriteLine("Peek at next item to dequeue: {0}",
numbers.Peek());
Console.WriteLine("Dequeuing '{0}'", numbers.Dequeue());
// Create a copy of the queue, using the ToArray method and the
// constructor that accepts an IEnumerable<T>.
Queue<string> queueCopy = new Queue<string>(numbers.ToArray());
Console.WriteLine("\nContents of the first copy:");
foreach( string number in queueCopy )
{
Console.WriteLine(number);
}
// Create an array twice the size of the queue and copy the
// elements of the queue, starting at the middle of the
// array.
string[] array2 = new string[numbers.Count * 2];
numbers.CopyTo(array2, numbers.Count);
// Create a second queue, using the constructor that accepts an
// IEnumerable(Of T).
Queue<string> queueCopy2 = new Queue<string>(array2);
Console.WriteLine("\nContents of the second copy, with duplicates and nulls:");
foreach( string number in queueCopy2 )
{
Console.WriteLine(number);
}
Console.WriteLine("\nqueueCopy.Contains(\"four\") = {0}",
queueCopy.Contains("four"));
Console.WriteLine("\nqueueCopy.Clear()");
queueCopy.Clear();
Console.WriteLine("\nqueueCopy.Count = {0}", queueCopy.Count);
}
}
/* This code example produces the following output:
one
two
three
four
five
Dequeuing 'one'
Peek at next item to dequeue: two
Dequeuing 'two'
Contents of the copy:
three
four
five
Contents of the second copy, with duplicates and nulls:
three
four
five
queueCopy.Contains("four") = True
queueCopy.Clear()
queueCopy.Count = 0
*/
using System.Collections.Generic;
class Example
{
public static void Main()
{
Queue<string> numbers = new Queue<string>();
numbers.Enqueue("one");
numbers.Enqueue("two");
numbers.Enqueue("three");
numbers.Enqueue("four");
numbers.Enqueue("five");
// A queue can be enumerated without disturbing its contents.
foreach( string number in numbers )
{
Console.WriteLine(number);
}
Console.WriteLine("\nDequeuing '{0}'", numbers.Dequeue());
Console.WriteLine("Peek at next item to dequeue: {0}",
numbers.Peek());
Console.WriteLine("Dequeuing '{0}'", numbers.Dequeue());
// Create a copy of the queue, using the ToArray method and the
// constructor that accepts an IEnumerable<T>.
Queue<string> queueCopy = new Queue<string>(numbers.ToArray());
Console.WriteLine("\nContents of the first copy:");
foreach( string number in queueCopy )
{
Console.WriteLine(number);
}
// Create an array twice the size of the queue and copy the
// elements of the queue, starting at the middle of the
// array.
string[] array2 = new string[numbers.Count * 2];
numbers.CopyTo(array2, numbers.Count);
// Create a second queue, using the constructor that accepts an
// IEnumerable(Of T).
Queue<string> queueCopy2 = new Queue<string>(array2);
Console.WriteLine("\nContents of the second copy, with duplicates and nulls:");
foreach( string number in queueCopy2 )
{
Console.WriteLine(number);
}
Console.WriteLine("\nqueueCopy.Contains(\"four\") = {0}",
queueCopy.Contains("four"));
Console.WriteLine("\nqueueCopy.Clear()");
queueCopy.Clear();
Console.WriteLine("\nqueueCopy.Count = {0}", queueCopy.Count);
}
}
/* This code example produces the following output:
one
two
three
four
five
Dequeuing 'one'
Peek at next item to dequeue: two
Dequeuing 'two'
Contents of the copy:
three
four
five
Contents of the second copy, with duplicates and nulls:
three
four
five
queueCopy.Contains("four") = True
queueCopy.Clear()
queueCopy.Count = 0
*/
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